The present invention relates to ambient noise removal device for detecting and canceling or removing noise sound around a headphone speaker or the like.
Heretofore, there have been proposed various techniques which, when a sound signal is to be reproductively output via a headphone speaker, reproduce the sound signal after canceling ambient noise (sound) around the speaker. Japanese Patent Application Laid-open Publication No. 2007-28354 (hereinafter referred to as “Patent Literature 1”) discloses a technique in accordance with which a microphone for detecting ambient noise sound is provided outside a casing of a headphone and noise sound is canceled by a headphone speaker being driven with a signal of an opposite phase from the noise signal detected by the microphone. Further, Japanese Patent No. 2822224 (hereinafter referred to as “Patent Literature 2”) discloses a technique in accordance with which a first microphone for detecting ambient noise sound is provided outside a casing of a headphone and a second microphone for detecting sound in an ear canal is provided inside the headphone so that an optimal noise canceling characteristic can always be obtained even when the way of wearing or attaching the headphone etc. has changed.
However, in cases where a microphone is used to detect ambient noise sound as in the aforementioned conventionally-known techniques, a microphone has to be mounted for each of left and right headphone casings, which would undesirably increase cost and increase the size of the headphone casings. Particularly, with the technique disclosed in Patent Literature 2, two microphones have to be mounted for each of the left and right headphone casings, which tends to difficult to realize if the headphones are small-size headphones, like a canal type.
Further, audio apparatus, such as headphone amplifiers, include an interface (headphone jack) for connection thereto a headphone. Where a sound signal is stereo signals, the interface generally has three terminals, and thus, if the headphone has a microphone mounted thereon, a noise signal detected by the microphone cannot be input to the audio apparatus. Therefore, in cases where a process for removing a noise signal detected by a microphone of a headphone is performed by such an audio apparatus, an ordinary- or conventional-type interface cannot be used as-is, so that it is necessary to provide a dedicated interface or a separate conversion device for converting the conventional-type interface.